In the description that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art.
In the field of semiconductor processing, plasma processing chambers are commonly used to etch one or more layers formed on a substrate. During etching, the substrate is supported on a substrate support surface within the chamber. Substrate supports can include edge rings positioned around the substrate support (i.e., around the substrate) for confining plasma to the volume above the substrate and/or to protect the substrate support, which typically includes a clamping mechanism, from erosion by the plasma. The edge rings, sometimes called focus rings, can be sacrificial (i.e., consumable) parts. Conductive and non-conductive edge rings are described in commonly-owned U.S. Pat. Nos. 5,805,408; 5,998,932; 6,013,984; 6,039,836 and 6,383,931.
Lithographic techniques can be used to form geometric patterns in a surface of a semiconductor substrate. During a lithographic process, a pattern such as an integrated circuit pattern can be projected from a mask or reticle and transferred to a photosensitive (e.g., photoresist) coating formed on a surface of the substrate. Plasma etching, in turn, can be used to transfer the pattern formed in the photoresist layer to one or more layers formed on the substrate that underlie the photoresist layer.
During plasma etching, plasma is formed above the surface of a substrate by adding large amounts of energy to a gas (or gas mixture) at low pressure. The plasma may contain ions, free radicals, and neutral species with high kinetic energies. By adjusting the electrical potential of the substrate, charged species in the plasma can be directed to impinge upon the surface of the substrate and thereby remove material (e.g., atoms) therefrom.
Plasma etching can be made more effective by using gases that are chemically reactive with the material to be etched. So called “reactive ion etching” combines the energetic etching effects of the plasma with the chemical etching effects of a reactive gas. However, during plasma etching, in addition to etching one or more layers of semiconductor material, the photoresist layer can also be removed by the plasma.
Residue from the photoresist and/or polymer that may form as an etching byproduct may undesirably redeposit on a lateral edge (e.g., bevel edge) or underside of the substrate. Bevel polymer, which may be volatilized during subsequent processing, may have an adverse effect on process yield. In order to maximize yield, reduction in polymer buildup at the underside and on the bevel edge of the substrate would be desirable.